US3084385A - Extrusion apparatus - Google Patents

Extrusion apparatus Download PDF

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US3084385A
US3084385A US825821A US82582159A US3084385A US 3084385 A US3084385 A US 3084385A US 825821 A US825821 A US 825821A US 82582159 A US82582159 A US 82582159A US 3084385 A US3084385 A US 3084385A
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edges
essential
lip
extrusion
divergence
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Heffelfinger Carl John
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EIDP Inc
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EI Du Pont de Nemours and Co
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29CSHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/25Component parts, details or accessories; Auxiliary operations
    • B29C48/30Extrusion nozzles or dies
    • B29C48/305Extrusion nozzles or dies having a wide opening, e.g. for forming sheets
    • B29C48/31Extrusion nozzles or dies having a wide opening, e.g. for forming sheets being adjustable, i.e. having adjustable exit sections
    • B29C48/313Extrusion nozzles or dies having a wide opening, e.g. for forming sheets being adjustable, i.e. having adjustable exit sections by positioning the die lips
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29CSHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/03Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
    • B29C48/07Flat, e.g. panels
    • B29C48/08Flat, e.g. panels flexible, e.g. films
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29CSHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/03Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
    • B29C48/09Articles with cross-sections having partially or fully enclosed cavities, e.g. pipes or channels
    • B29C48/10Articles with cross-sections having partially or fully enclosed cavities, e.g. pipes or channels flexible, e.g. blown foils

Definitions

  • the invention will be described as it applies to hat film in the form :of sheets and the like. However, it should be understood that the invention is applicable to the extrusion of lilm in tubular form, as narrow ribbons or in any other form wherein .the buildup lof degraded polymer on 'the oriice-delining lip members poses a problem.
  • the impnovement in design that is the subject lof the present invention comprises a pair of partially parallel, partially -diverging essential edges of lip members of depth 1), the mutual divergence of said essential edges being vfor a distance equal to about 0.5- 0% -of the depth 3), the divergence terminating at the plane containing the lines defining ⁇ the outermost edges of said lip member-s and the divergence of each essential edge being such that a straight line drawn from the 'outermost ⁇ edge of the lip member to the point at which divergence starts makes Ian angle of -60 degrees with the plane defined by the extension ⁇ of the parallel portions of said essential edges of the lip member-s.
  • the divergence may take the preferred form of a straight line in each lip member, ie., chamfered or beveled edges, or each edge may be rounded to present a pair of convex surfaces. If each edge is rounded, itis preferred that the roundness be formed according 'to a regular geometric pattern so that the rounded surface represents a section of an ellipsoid, hyperboloid, paraboloid or cylinder.
  • FIGURE 1 is a side elevation with parts in section of the extrusion apparatus
  • FIGURE 2 is a chess-sectional view taken substantially along the line 2--2 of FIGURE 1',
  • FIGURE 3 is ran enlarged sectional View of the essential edges of hopper lips within the scope of the present invention.
  • FIGURE 4 is an enlarged sectional view of another modilication within the scope of the present invention of the essential edges lof the hopper lips; land FIGURE 5 yis an enlarged sectional view of the essential edges of hopper lips of the prior art.
  • the film extrusion apparatus comprises a main body member 1 composed of 1a metal having a flat bottom Z.
  • An enlarged U-shaped longitudinal channel 3 is located in the center [of the body, the spaced side walls of the channel terminating in two longitudinal edges where they meet 'the bottom.
  • Fitted in channel 3 is a ⁇ similarly shaped longitudinal sleeve 4.
  • the side wells of this sleeve are welded to the body member at the longitudinal edges where the channel meets the bottom wall.
  • the lengthwise opening. 5 between the sleeve edges constitutes .a wide tone or
  • the outer Wall of the sleeve is spaced from the channel walls .so .as to provide a space for the circulation of a heat-exchange lluid.
  • a plurality of diagonal passages 6 communicate with said -space and with horizontal ⁇ passagers 7 in end plates 8 which are Iheld to body member 1 by means of bolts 9.
  • Aixed to each end plate 'by a weld joint is a bell-shaped hub 10 which is adapted to receive la metal tube 11 having ⁇ a flared or frustroconical portion i12. the inner end of which abuts the end fof sleeve .4.
  • the hub has ⁇ a smooth cylindrical portion 13 which is journalled in a suitable bearing on a frame (not shown).
  • the end yof the hub is shaped to receive a cap 14 which has a hole 15 interlitting with the outer surface of the tube.
  • This cap can be fixed to the hub by means of screw threads, a weld, or other suitable means, or it can be force-fitted onto the hub.
  • a worm gear 16 is placed over one cap and attached to it by a suitable means, for example by means of screw V17' threadably engaged with lug 18 on the collar.
  • the outer walls of tube l1 are ⁇ spaced from the inner Walls of the bellshaped hub for the circulation of la heat-exchange fluid.
  • a plurality of openings 19 are provided in the ends of the cap and they communicate with a suitable source of heat-exchange Huid.
  • The' other hub has a collar 2@ with a lug 20 which can be fastened yto 'a frame member after the hubs and assoeiated extrusion device are adjusted, by means of the worm gear and associated means (not shown), to the desired position.
  • each lip member 2l has a flat upper surface which tits against the llat bottom surface 2 of the body member 1.
  • the upper arm is provided with a row of holes 23 preferably uniformly spaced through which extend screws 24.
  • the dat inner heads of the screws contact the inner surface of the upper arm and the heads are disposed in lateral open-ended slot 25. These screws are threadably engaged with suitable threaded holes 26 in the bottom surface of the body member.
  • bottom arm 27 immediately beneath each screw head is a hole 2S for the insertion of a tool to adjust the screws.
  • a narrow lateral slot 29 extends from each hole to the outer edge of the lower arm of the U-shaped member 2l.
  • each lip member 21 slants for most of its length and together they form a tapered orifice to lead fluid from the channel sleeve to the Harley-delining lip portions or essential edges 31 of the end walls of the lip members 21.
  • Screws 32 which are thread'ably'engaged in respective holes 33 in the upper arm extend through similarly spaced holes 34 (of larger diameter than the screws) in bottom arm 27. IBetween the head of each screw 32 and the outer surface of the arm is a washer 35 and a coil spring ⁇
  • the open ends of slot 25 i.e., between the upper arm 22 and bottom arm 27
  • These threaded arcs have their bisecting Vertical plane passing through the center of screws.
  • Threadably engaged with the arcuate portions are tapered screws 38 having polygonal shaped ends 39 adapted to receive a tool (not shown) for adjusting them toward or away from the longitudinal axis of the extrusion grout.
  • Each spring insures that each segment ot the lower arm between nar-row lateral slots 29 is always in contact with the tapered screw in the central part of such segment.
  • the taper of the thread, the pitch of the thread and the lever ratio can be selected to give the desired mechanical advantage Ibetween screw rotation and lip movement. While in the preferred aspect of the invention there are two adjustable extrusion orifice-delining members, one of these can be made solid and nonexible.
  • the lip members 21 are fastened in the body member by first aligning the essential edges of the lips along an axis at approximately the spacing desired and then tightening t-he screws 24. The Width of the slot opening between the lips in each segment between narrow -slots 29 is measured carefully. Tapered screws 38 are then adjusted to correct for any deviations from a straight line.
  • FIGURE is an enlarged sectional view of the essential suddenly-dening edges of the lip members 21, as known heretofore in the prior art. It will be noted that the perennial-deiining edges 311 are ilat and mutually parallel throughout the depth D.
  • FIGURE 3 is an enlarged section showing the same oriiice-deiining portion of lip members 21 as in FIGURE 5 but constructed in accordance with the preferred mode ot the present invention.
  • the orifice-defining essential edges 31 are mutually parallel for a distance less than the total depth D.
  • the lip portions start to mutually diverge.
  • the angle of divergence a being from 60 degrees.
  • the distance over which the essential suddenly-dening edges of the lip members diverge should be less than one-half of the total depth D of the essential edges, i.e., less than 50% of D.
  • the minimum distance of divergence is preferably 2% oi the total depth D of the essential edges. However, divergence for a distance ment in the smoothness of the extrusion operation.
  • FIGURE 4 represents another embodiments wherein* the edges have been rounded to form a section of a cyl-v inder.
  • the mutually divergent portions starting at B and B' and the angle of divergence b should be the same as for FIGURE 3. That is, the lip portions should diverge over a distance equal to 0.5-50% of the total depth of their essential edges" and at an angle of 10-6() degrees.
  • EXAMPLE 1-3 polyethylene terephthalate polymer prepared as described in USL Patent No. 2,465,319 to Whin-eld and Dickson was continuously extruded at a rate of about 1,000 pounds/hour at a temperature of 280 C. through an extrusion die of conventional design to form iilm having a thickness of 5-20 mils.
  • the geometry of the orifice-defining essential edges of the die lips was modified in Examples 1 3, in accordance with the present invention.
  • the total depth of the exit orifice, i.e., D was 0.125.
  • Example l the lips mutually diverge to form a cylindrical (rounded) surface similar to that illustrated in FIGURE 4 of radius 0.0078; in Example 2, to form a cylindrical surace similar to that illustrated in FIGURE 4 of radius 0.0156; and in Example 3, to form a planar (chamfered) surface as illustrated in FIGURE 3 of depth 0.0156" having an angle of chamfer of 30 degrees.
  • the exit path defining surface of the die lips (the effective essential edge or land) having a depth of 0.125 was conventional, i.e., of the square geometry shown in FIGURE 5.
  • Polyethylene terephthalate polymer was extruded continuously through this special extrusion die over periods of time ranging from 1.5-8.5 hours, With the temperature of the molten polymer and the extrusion rate being varied to simulate a range of process conditions. Table ll, be-
  • EXAMPLE 8 Polyethylene terephthalate polymer was prepared as in Example 1. The polymer was extruded at a temperature of 280 C. through a conventional extrusion die with the modification that the essential edges at the exit of the die lips were chamfered at a 30 angle with a chamfered depth of 0.0156", the total depth of the orificedeiining essential edges being 0.125. The lip opening was 0.035". Test runs ⁇ of 24 hours duration Were made. Results of the performance of this extrusion die are listed in Table lll compared to control runs in which an extrusion die with oriee-deiining lips of regular square geometry was used.
  • EXAMPLE 9 Polyethylene terephthalate polymer prepared as described in Example 1 was continuously extruded through a conventional extrusion die in which the exit defining lips (the essential edges of the lip members) of the die had a cylindrical coniiguration with a radius of 0.0156". The extrusion die lip opening was 0.013". The depth of the essential edge was 0.1094". As a control, the polyethylene terephthalate polymer was melt extruded through an extrusion die having the conventional square exit lip geometry.
  • an extrusion apparatus for the extrusion of molten polymeric material in the form of a film wherein the exit path of the extrudate is defined by the orificedefining essential edges of a pair of lip members, the improvement which comprises a pair of lip members, the essential edges of sai-d lip members being partially parallel and partially diverging, the divergence of Said essential edges being for a distance equal to about (L5-50% of the total depth of said essential edges, the parallel portions of said essential edges being from about 50-99.5% of the total depth of said essential edges, said divergence terminaitng vat the plane containing the lines defining the outermost edges of said lip members, the divergence of each essential edge being such that a straight line drawn from the outermost edge of the lip member to the point at which divergence starts makes an angle of 10-60 degrecs with the plane dened by the extension of the parallel portions of said essential edges of the lip members.
  • an extrusion apparatus for the extrusion of molten polymeric material in the form of a iilm wherein the exit path of the extrudate is defined by the orifice-defining essential edges o ⁇ a pair of lip members, the improvement which comprises a pair of lip members, the essential edges of said lip members being partially parallel and partially diverging, the divergence ot said essential edges being for a distance equal to about 2-50% of the total ⁇ depth of said essential edges, the parallel portions of said essential edges being from about 50-98% of the total depth of said essential edges, said divergence terminating at the plane containing the lines defining the outermost edges of said lip members, the divergence of each essential edge being such that a straight line drawn from the outermost edge of the lip member to the point at Which divergence starts makes an angle of 10-60 degrees with the plane defined by the extension of the parallel portions of said essential edges ot the lip members.

Description

April 9, 1963 c. J. HEFFELFINGER 3,084,385
ExTRusIoN APPARATUS 2 Sheets-Sheet 1 Filed July 8, 1959 mi IIIIII INVENTOR CARL JHN HEFFELFNGER LQ n ATTORNEY April 9, 1963 c. .1.HEFFELF1NGl-:R 3,084,385
ExTRUsIoN APPARATUS Filed July 8, 1959 2 Sheets-Sheet 2 ETW 33 www@ 39 Fig. 5
HWENTOR CARI. JOHN HEFFELF/NGER BY @4A/M 972@ ATTORNEY United States Patent Oiiice 3,084,385 Patented Apr. 9, 1963 3,034,385 EXTRUSEQN APPARATUS Sarl .lohn Heeiiinger, Circlevillc, hie, assigner to E. I. Pont de l Temours and Company, Wilmington, Del., a corporation of ieiaware Filed .idly 8, 1959, Ser. No. 325,321 4 Caims. (Cl. it-lil This invention relates to apparatus for the continuous extrusion of films. More particularly, it relates to an improved die design for an extrusion apparatus.
In the preparation of self-supporting iilms from polymeric thermoplastic materials, it is usual to extrude the polymeric material in molten form through an extrusion die and to cast the extruded polymer as a lilm onto a quenching device. For example, m-olten polyethylene terephthalate is cast as a iilm through an extrusion die (hopper) consisting of la slot with parallel faces that are adjustable over their length.
One clitculty which arises in polyethylene terephthalate extrusion and which would also ari-se in the extrusion of most molten polymers through an extrusion die is that degraded polymer tends .to build up on the lips -of the die. This is caused by low molecular weight materials wetting the emergent lip and baking on the surface at the temperatures used. The presence of degraded polymer on the die lips produces ilow deformities during extrusion. The flow deformities manifest themselves as streaks or smears in the cast iilrn. This condition is corrected only by stopping operation and manually cleaning the die lips. A substantial loss of material and time is reflected in the high cost of producing such ilms.
It is an object of this invention to pnovide an irnproved apparatus for the extrusion of thin films. Another object is to provide an apparatus which produces thin films of substantially uniform thickness over extended periods of operation. Other objects will appear hereinafter.
The objects 'are accomplished by a novel design for the co-acting lip members which deiine the slot or orice of the extrusion die, through which orifice the molten polymer is extruded.
The invention will be described as it applies to hat film in the form :of sheets and the like. However, it should be understood that the invention is applicable to the extrusion of lilm in tubular form, as narrow ribbons or in any other form wherein .the buildup lof degraded polymer on 'the oriice-delining lip members poses a problem.
in an extrusion apparatus of the slotted die type suitable for the extrusion of molten polymeric material in the form of la film wherein the exit path of the extrudate is deiined by the orifice-defining essential edges of a pair of lip members, the impnovement in design that is the subject lof the present invention comprises a pair of partially parallel, partially -diverging essential edges of lip members of depth 1), the mutual divergence of said essential edges being vfor a distance equal to about 0.5- 0% -of the depth 3), the divergence terminating at the plane containing the lines defining `the outermost edges of said lip member-s and the divergence of each essential edge being such that a straight line drawn from the 'outermost `edge of the lip member to the point at which divergence starts makes Ian angle of -60 degrees with the plane defined by the extension `of the parallel portions of said essential edges of the lip member-s.
The divergence may take the preferred form of a straight line in each lip member, ie., chamfered or beveled edges, or each edge may be rounded to present a pair of convex surfaces. If each edge is rounded, itis preferred that the roundness be formed according 'to a regular geometric pattern so that the rounded surface represents a section of an ellipsoid, hyperboloid, paraboloid or cylinder.
The invention will be more clearly understood by referring to the drawings which follow, in which:
FIGURE 1 is a side elevation with parts in section of the extrusion apparatus;
FIGURE 2 is a chess-sectional view taken substantially along the line 2--2 of FIGURE 1',
FIGURE 3 is ran enlarged sectional View of the essential edges of hopper lips within the scope of the present invention;
FIGURE 4 is an enlarged sectional view of another modilication within the scope of the present invention of the essential edges lof the hopper lips; land FIGURE 5 yis an enlarged sectional view of the essential edges of hopper lips of the prior art.
Referring now to FlGURES l and 2, the film extrusion apparatus comprises a main body member 1 composed of 1a metal having a flat bottom Z. An enlarged U-shaped longitudinal channel 3 is located in the center [of the body, the spaced side walls of the channel terminating in two longitudinal edges where they meet 'the bottom. Fitted in channel 3 is a `similarly shaped longitudinal sleeve 4. The side wells of this sleeve are welded to the body member at the longitudinal edges where the channel meets the bottom wall. The lengthwise opening. 5 between the sleeve edges constitutes .a wide orice or |outlet from the sleeve. The outer Wall of the sleeve is spaced from the channel walls .so .as to provide a space for the circulation of a heat-exchange lluid. A plurality of diagonal passages 6 communicate with said -space and with horizontal `passagers 7 in end plates 8 which are Iheld to body member 1 by means of bolts 9. Aixed to each end plate 'by a weld joint is a bell-shaped hub 10 which is adapted to receive la metal tube 11 having `a flared or frustroconical portion i12. the inner end of which abuts the end fof sleeve .4. The hub has `a smooth cylindrical portion 13 which is journalled in a suitable bearing on a frame (not shown). The end yof the hub is shaped to receive a cap 14 which has a hole 15 interlitting with the outer surface of the tube. This cap can be fixed to the hub by means of screw threads, a weld, or other suitable means, or it can be force-fitted onto the hub. A worm gear 16 is placed over one cap and attached to it by a suitable means, for example by means of screw V17' threadably engaged with lug 18 on the collar. The outer walls of tube l1 are `spaced from the inner Walls of the bellshaped hub for the circulation of la heat-exchange fluid. A plurality of openings 19 are provided in the ends of the cap and they communicate with a suitable source of heat-exchange Huid.
The' other hub has a collar 2@ with a lug 20 which can be fastened yto 'a frame member after the hubs and assoeiated extrusion device are adjusted, by means of the worm gear and associated means (not shown), to the desired position.
Beneath the body member and fastened thereto on each side of the lengthwise slot opening 5 in the channel sleeve, there are disposed two co-acting lip members 21 which are U-shaped and substantially identical in construction except that they are reversed in position. The upper arm 22 of each lip member 2l has a flat upper surface which tits against the llat bottom surface 2 of the body member 1. The upper arm is provided with a row of holes 23 preferably uniformly spaced through which extend screws 24. The dat inner heads of the screws contact the inner surface of the upper arm and the heads are disposed in lateral open-ended slot 25. These screws are threadably engaged with suitable threaded holes 26 in the bottom surface of the body member.
In bottom arm 27 immediately beneath each screw head is a hole 2S for the insertion of a tool to adjust the screws. A narrow lateral slot 29 extends from each hole to the outer edge of the lower arm of the U-shaped member 2l.
The bottom web or inner end walls 30 ot each lip member 21 slants for most of its length and together they form a tapered orifice to lead fluid from the channel sleeve to the orice-delining lip portions or essential edges 31 of the end walls of the lip members 21.
Screws 32 which are thread'ably'engaged in respective holes 33 in the upper arm extend through similarly spaced holes 34 (of larger diameter than the screws) in bottom arm 27. IBetween the head of each screw 32 and the outer surface of the arm is a washer 35 and a coil spring` The open ends of slot 25 (i.e., between the upper arm 22 and bottom arm 27) have threaded arcuate portions 37 in the surfaces of such arms. These threaded arcs have their bisecting Vertical plane passing through the center of screws. Threadably engaged with the arcuate portions are tapered screws 38 having polygonal shaped ends 39 adapted to receive a tool (not shown) for adjusting them toward or away from the longitudinal axis of the extrusion orice. Each spring insures that each segment ot the lower arm between nar-row lateral slots 29 is always in contact with the tapered screw in the central part of such segment. The taper of the thread, the pitch of the thread and the lever ratio can be selected to give the desired mechanical advantage Ibetween screw rotation and lip movement. While in the preferred aspect of the invention there are two adjustable extrusion orifice-delining members, one of these can be made solid and nonexible.
In assembling the device, the lip members 21 are fastened in the body member by first aligning the essential edges of the lips along an axis at approximately the spacing desired and then tightening t-he screws 24. The Width of the slot opening between the lips in each segment between narrow -slots 29 is measured carefully. Tapered screws 38 are then adjusted to correct for any deviations from a straight line.
FIGURE is an enlarged sectional view of the essential orice-dening edges of the lip members 21, as known heretofore in the prior art. It will be noted that the orice-deiining edges 311 are ilat and mutually parallel throughout the depth D.
FIGURE 3 is an enlarged section showing the same oriiice-deiining portion of lip members 21 as in FIGURE 5 but constructed in accordance with the preferred mode ot the present invention. The orifice-defining essential edges 31 are mutually parallel for a distance less than the total depth D. At points A and A', the lip portions start to mutually diverge. The angle of divergence a being from 60 degrees., The distance over which the essential orice-dening edges of the lip members diverge should be less than one-half of the total depth D of the essential edges, i.e., less than 50% of D. Divergence for a distance greater than 50% of D provides too low a pressure drop across the lip and produces varying llow patterns along the length of the orilice, i.e., across the width of the extruded film. Both of these factors yield non-uniform, unacceptable films. The minimum distance of divergence is preferably 2% oi the total depth D of the essential edges. However, divergence for a distance ment in the smoothness of the extrusion operation.
FIGURE 4 represents another embodiments wherein* the edges have been rounded to form a section of a cyl-v inder. However, the mutually divergent portions starting at B and B' and the angle of divergence b should be the same as for FIGURE 3. That is, the lip portions should diverge over a distance equal to 0.5-50% of the total depth of their essential edges" and at an angle of 10-6() degrees.
The principles and practice of the present invention will be more clearly understood by referring to the ex amples which follow. Although these examples relate tol the extrusion of polyethylene terephthalate iilm, other' kinds of materials can also be extruded in the apparatus ot the present invention with the same success obtained using polyethylene terephthalate. Among such materials are film-forming polymers such as polyethylene, polyvinyl chloride, copolymers of vinyl chloride and vinyl acetate, polyvinyl fluoride, polymethyl methacrylate, polystyrene, regenerated cellulose, cellulose acetate, cellulose propionate, cellulose acetate butyrate, ethyl cellulose, rubber hydrochloride, etc.
EXAMPLE 1-3 In Examples h3, polyethylene terephthalate polymer prepared as described in USL Patent No. 2,465,319 to Whin-eld and Dickson was continuously extruded at a rate of about 1,000 pounds/hour at a temperature of 280 C. through an extrusion die of conventional design to form iilm having a thickness of 5-20 mils. The geometry of the orifice-defining essential edges of the die lips was modified in Examples 1 3, in accordance with the present invention. The total depth of the exit orifice, i.e., D, was 0.125. In Example l, the lips mutually diverge to form a cylindrical (rounded) surface similar to that illustrated in FIGURE 4 of radius 0.0078; in Example 2, to form a cylindrical surace similar to that illustrated in FIGURE 4 of radius 0.0156; and in Example 3, to form a planar (chamfered) surface as illustrated in FIGURE 3 of depth 0.0156" having an angle of chamfer of 30 degrees. As a control, the exit path defining surface of the die lips (the effective essential edge or land) having a depth of 0.125 was conventional, i.e., of the square geometry shown in FIGURE 5.
The smoothness or continuity of operation for each case is given in Table II. The extrusion operation was stopped in order to clean the die lips when unreasonable streaks or smears appeared in the cast lm.
EXAMPLES 4-7 In order to eiect a simultaneous comparison between the lip geometry of the present invention and the conventional square lip geometry under identical process conditions, a special extrusion die -was constructed wherein the orice-dening lip structure was 21" in length, the geometry of the exit-defining lips differing over three 7" sections. One edge section had a 15 chamfer with a chamfer depth of 0.0l56; the center section, a conventional (square) lip geometry; and the other edge section, a 30 chamfer with a chamfer depth of 0.0156", the total depth of the orice-defning essential edge being 0.125.
Polyethylene terephthalate polymer was extruded continuously through this special extrusion die over periods of time ranging from 1.5-8.5 hours, With the temperature of the molten polymer and the extrusion rate being varied to simulate a range of process conditions. Table ll, be-
low, lists the incidence of smears (average number of smears per hour) for polymer extruded through `each of the three sections of the extrusion die described above. Table II v Polymer Temper- Length Av erage Ex. Lip Geometry Extruded ature of oi Run No.
of Section (lbs/hr.) Extrusion (Hr.) Smears C.) per Hour d- 4 15u cheminer. 150 200 8.5 1.8
emmer--. 150 aso a5 4.3 15 square 150 290 S. 5 14.-. 5 5 15 eharnfen-. 150 280 2.5 0 30 chantier... 150 280 2. 5 0 square 150 280 2. 5 14 6 15 chamfe 100 280 1.5 0.5 30 charmer. 100 280 1.5 0.5 square- 100 280 1. 5 12 20 7 15 chamier-.. 100 290 0.0 0
30 chamfer". 100 200 6. 0 0. 25 square 100 290 G. 0 2
EXAMPLE 8 Polyethylene terephthalate polymer was prepared as in Example 1. The polymer was extruded at a temperature of 280 C. through a conventional extrusion die with the modification that the essential edges at the exit of the die lips were chamfered at a 30 angle with a chamfered depth of 0.0156", the total depth of the orificedeiining essential edges being 0.125. The lip opening was 0.035". Test runs `of 24 hours duration Were made. Results of the performance of this extrusion die are listed in Table lll compared to control runs in which an extrusion die with oriee-deiining lips of regular square geometry was used.
Table Ill Thiek- Number Average Die Lip Rate o ness of Lip Streak Test Run Geometry Polymer (gauge) Clean- Grade 1 Employed Extrudoi Cast ings per per ed/hour Film 24 hrs. 24 hours (mils) W4 Controls:
A Square 900 5l0 4 2. 1
do 1,000 10 S 3. 5
lStreak grade-The incidence ol streaks occurring in the east film was noted and the film graded from 0-5 according to the severity oi streak incidence; a streak grade of 0 indicating no streak formation.
EXAMPLE 9 Polyethylene terephthalate polymer prepared as described in Example 1 was continuously extruded through a conventional extrusion die in which the exit defining lips (the essential edges of the lip members) of the die had a cylindrical coniiguration with a radius of 0.0156". The extrusion die lip opening was 0.013". The depth of the essential edge was 0.1094". As a control, the polyethylene terephthalate polymer Was melt extruded through an extrusion die having the conventional square exit lip geometry.
The comparison of the results obtained in several tests using these two geometric configurations is summarized in Table 1V.
Tab ze 1V Mfr/ff# Smear Rate of Tempera- Frequency Die Lip Geometry Employed Polymer ture of (average E xtrnded Extrusion number (lhs/hr.) C.) o smears per hour) Square 150 290 135 Rounded. 150 290 1 Square 150 285 140 Rounde 150 285 4. 3 Square 150 280 170 Rounded 150 280 19 Square 150 290 355 Rounded- 150 290 13 Square- 150 290 94. 5 Rounded. 150 290 5. 8 Square- 290 137 Rounde 100 290 6. 8
Having fully disclosed the invention, what is claimed is:
1. ln an extrusion apparatus for the extrusion of molten polymeric material in the form of a film wherein the exit path of the extrudate is defined by the orificedefining essential edges of a pair of lip members, the improvement which comprises a pair of lip members, the essential edges of sai-d lip members being partially parallel and partially diverging, the divergence of Said essential edges being for a distance equal to about (L5-50% of the total depth of said essential edges, the parallel portions of said essential edges being from about 50-99.5% of the total depth of said essential edges, said divergence terminaitng vat the plane containing the lines defining the outermost edges of said lip members, the divergence of each essential edge being such that a straight line drawn from the outermost edge of the lip member to the point at which divergence starts makes an angle of 10-60 degrecs with the plane dened by the extension of the parallel portions of said essential edges of the lip members.
2. An extrusion apparatus as in claim l wherein the divergence of the essential edges of the lip members is in the form of chamfered edges.
3. An extrusion apparatus as in claim 1 wherein the divergence of the essential edges of the lip members is in the form of cylindrically rounded edges.
4. ln an extrusion apparatus for the extrusion of molten polymeric material in the form of a iilm wherein the exit path of the extrudate is defined by the orifice-defining essential edges o `a pair of lip members, the improvement which comprises a pair of lip members, the essential edges of said lip members being partially parallel and partially diverging, the divergence ot said essential edges being for a distance equal to about 2-50% of the total `depth of said essential edges, the parallel portions of said essential edges being from about 50-98% of the total depth of said essential edges, said divergence terminating at the plane containing the lines defining the outermost edges of said lip members, the divergence of each essential edge being such that a straight line drawn from the outermost edge of the lip member to the point at Which divergence starts makes an angle of 10-60 degrees with the plane defined by the extension of the parallel portions of said essential edges ot the lip members.
References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. IN AN EXTRUSION APPARATUS FOR THE EXTRUSION OF MOLTEN POLYMERIC MATERIAL IN THE FORM OF A FILM WHEREIN THE EXIT PATH OF THE EXTRUDATE IS DEFINED BY THE ORIFICEDEFINING ESSENTIAL EDGES OF A PAIR OF LIP MEMBERS, THE IMPROVEMENT WHICH COMPRISES A PAIR OF LIP MEMBERS, THE ESSENTIAL EDGES OF SAID LIP MEMBERS BEING PARTIALLY PARALLEL AND PARTIALLY DIVERGING, THE DIVERGENCE OF SAID ESSENTIAL EDGES BEING FOR A DISTANCE EQUAL TO ABOUT 0.5-50% OF THE TOTAL DEPTH OF SAID ESSENTIAL EDGES, THE PARALLEL PORTIONS OF SAID ESSENTIAL EDGES BEING FROM ABOUT 50-99.5% OF THE TOTAL DEPTH OF SAID ESSENTIAL EDGES, SAID DIVERGENCE TERMINATING AT THE PLANE CONTAINING THE LINES DEFINING THE OUTERMOST EDGES OF SAID LIP MEMBERS, THE DIVERGENCE OF EACH ESSENTIAL EDGE BEING SUCH THAT A STRAIGHT LINE DRAWN FROM THE OUTERMOST EDGE OF THE LIP MEMBER TO THE POINT AT WHICH DIVERGENCE STARTS MAKES AN ANGLE OF 10-60 DEGREES WITH THE PLANE DEFINED BY THE EXTENSION OF THE PARALLEL PORTIONS OF SAID ESSENTIAL EDGES OF THE LIP MEMBERS.
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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3354505A (en) * 1964-05-14 1967-11-28 Roehm & Haas Gmbh Extrusion die
US5273420A (en) * 1990-11-05 1993-12-28 Roehm Gmbh Chemische Fabrik Extrusion die for thermoplastic webs
US6926512B2 (en) * 1998-09-03 2005-08-09 Bp Corporation North America Inc. Apparatus for extruding foamed polypropylene sheet having improved surface appearance
FR2938205A1 (en) * 2008-11-07 2010-05-14 Michelin Soc Tech DOUBLE PROFILE EXTRUSION LINE

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1800180A (en) * 1929-11-06 1931-04-07 Goodyear Tire & Rubber Method of preventing overheating of rubber in screw-type extruding machines
US2341749A (en) * 1942-03-14 1944-02-15 Arthur M Webb Extrusion die
CA451864A (en) * 1948-10-12 Edward Maier Robert Extrusion process and apparatus
US2659103A (en) * 1951-08-23 1953-11-17 Eastman Kodak Co Knee action dope hopper finger
US2677148A (en) * 1950-06-02 1954-05-04 American Viscose Corp Spinneret
US2765492A (en) * 1955-02-23 1956-10-09 Du Pont Extrusion apparatus
US2923969A (en) * 1960-02-09 Certificate of correction

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA451864A (en) * 1948-10-12 Edward Maier Robert Extrusion process and apparatus
US2923969A (en) * 1960-02-09 Certificate of correction
US1800180A (en) * 1929-11-06 1931-04-07 Goodyear Tire & Rubber Method of preventing overheating of rubber in screw-type extruding machines
US2341749A (en) * 1942-03-14 1944-02-15 Arthur M Webb Extrusion die
US2677148A (en) * 1950-06-02 1954-05-04 American Viscose Corp Spinneret
US2659103A (en) * 1951-08-23 1953-11-17 Eastman Kodak Co Knee action dope hopper finger
US2765492A (en) * 1955-02-23 1956-10-09 Du Pont Extrusion apparatus

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3354505A (en) * 1964-05-14 1967-11-28 Roehm & Haas Gmbh Extrusion die
US5273420A (en) * 1990-11-05 1993-12-28 Roehm Gmbh Chemische Fabrik Extrusion die for thermoplastic webs
US6926512B2 (en) * 1998-09-03 2005-08-09 Bp Corporation North America Inc. Apparatus for extruding foamed polypropylene sheet having improved surface appearance
FR2938205A1 (en) * 2008-11-07 2010-05-14 Michelin Soc Tech DOUBLE PROFILE EXTRUSION LINE
WO2010052186A1 (en) * 2008-11-07 2010-05-14 Societe De Technologie Michelin Dual profile extrusion die

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